This invention relates to internal combustion engines, and more particularly to a piston construction having improved means for restricting end play of the pin that connects the piston to an associated connecting rod. The invention can be used in sparkxe2x80x94ignition gasoline engines or pressurexe2x80x94ignition diesel engines.
In many internal combustion engines the pistons are operatively connected to the associated connecting rods by piston pins. Each piston pin extends through aligned openings in the piston and the connecting rod, to establish a pivotal connection between the rod and piston. As the engine crankshaft rotates, one end of each connecting rod orbits around the drive shaft axis. The other end of the connecting rod has a swivel motion around the pin within the piston, whereby each connecting rod delivers power between the crankshaft and each associated piston. Each piston pin serves as a pivotal connection between the connecting rod and piston.
In one particular piston design the piston is an articulated piston having a two piece construction. A major component of the piston forms the piston head and the piston skirt. Struts extending down from the piston head forms two spaced bearings for the piston pin. One end of an associated connecting rod extends into the space between the bearings, whereby the piston pin can be extended through the end of the connecting rod and the spaced bearings, to form a pivotal connection between the connecting rod and piston.
In order to install the piston pin in the piston the pin has to be moved into its final position after the connecting rod is inserted into the piston. Typically, the piston has aligned openings in the piston side wall to permit the piston pin to be inserted into the piston. The piston has a floating orientation in the aligned bearings in the piston and connecting rod, such that the pin can shift on the pin axis so as to possibly contact the surface of the combustion cylinder. Such contact is undesirable in that the cylinder surface can wear or degrade. Minute metal particles formed by the wear action can generate further wear of the cylinder surface.
To prevent shifting (or play) of the piston pin it is a common practice to provide snap rings at the ends of the pin. Each snap ring fits into an annular groove in an opening in the piston side wall to form an obstruction at an end surface of the piston pin. The piston pin is located between the two snap rings so that the pin cannot shift along the pin axis.
The snap rings perform the intended function. However, such snap rings utilize space along the piston pin axis, such that the pin is somewhat shortened. The relatively shorter pin reduces the available bearing length, which can undesirably reduce the expected service life of the piston or piston pin.
The present invention relates to a mechanism for reducing end play of the piston pin without unduly shortening the piston pin. The longer piston pin can result in a greater bearing length and bearing surface area.
In one form of the invention the mechanism for limiting end play of the piston pin includes two end caps secured to opposite ends of the pin. Each end cap has a spherical surface facing the side wall of the combustion cylinder. These spherical flanges extend beyond the piston diameter and are spaced apart by a distance that is slightly more than surfaces 42, 42 of FIG. 2 of the piston, so that any tendency of the piston pin to shift along the pin axis causes one of the flange surfaces to contact the piston wall 42. There is no contact with the cylinder wall. This method of retention also prevents the piston pin from falling out prior to piston assembly into the cylinder bore.
Each end cap includes a plug section telescoped into a recess in an end surface of the piston pin, whereby the cap is secured to the pin without unduly shortening the pin. The longer pin enables the piston to be designed so as to provide a relatively longer pin bearing length.
In another form of the invention, the mechanism for limiting pin end play involves forming the pin with spherical end surfaces. The spacing between these spherical surfaces is slightly less than the piston diameter, so that any tendency of the pin to shift along the pin axis causes one of the spherical surfaces to contact the cylinder side wall. Each spherical surface has sufficient area as to prevent wear of the cylinder wall or spherical surface. This form of the invention maximizes the length of the piston pin, but presents the problem of an unrestrained sub-assemble.